I picked up a Toyo View conpendium hood relatively inexpensively at a camera show. Overall dimensions of the frame for it are about 155mm square (just over 6x6") with an opening of about 125mm square (5x5"). That should handle the filter sizes you are talking about.

I am looking at using the front to mount the 8x10 or 8x20 format mask, and a seond mask on the frame nearest the lens with a circular opening to handle filters in a Calumet Xenphon filter holder for either 4x4 or 3x3 rectangular filters. Both masks looking at using velcro to mount the masks and be able to repostion them.

The funky issue is fitting them onto two very different and old wood cameras without modifying the cameras themselves...